Historically, the telecommunications industry has developed separately and largely independently from the computing industry. Conventional telecommunications systems are characterized by having high reliability circuit switched networks for communicating over long distances, whereas data communications between communicating computers is largely based upon shared access packet communications.
Datacoms may operate over a local area, to form a local area network (LAN) or over a wide area to form a wide area network (WAN). Historically the difference between a LAN and a WAN is one of geographical coverage. A LAN may cover communicating computing devices distributed over an area of kilometers or tens of kilometers, whereas a WAN may encompass communicating computing devices distributed over a wider geographical area, of the order of hundreds of kilometers or greater.
However, the historical distinction between local area networks and wide area networks is becoming increasingly blurred.
Conventional local area networks are generally taken to be digital data networks operating at rates in excess of 1 MBits/s over distances of from a few meters up to several kilometers. Conventional local area networks are almost universally serial systems, in which both data and control functions are carried through the same channel or medium. Local area networks are primarily data transmission systems intended to link computer devices and associated devices within a restricted geographical area. However, many local area networks include speech transmission as a service. A plurality of computer and associated devices linked together in a LAN may range from anything from a full-scale mainframe computing system to a collection of small personal computers. Since a local area network is confined to a restricted geographical area, it is possible to employ vastly different transmission methods from those commonly used in telecommunications systems. Local area networks are usually specific to a particular organization which owns them and can be completely independent of the constraints imposed by public telephone authorities, the ITU, and other public services. Local area networks are characterized by comprising inexpensive line driving equipment rather than the relatively complex modems needed for public analog networks. High data transmission rates are achieved by utilizing the advantages of short distance.
On the other hand, conventional wide area networks operate in general on a greater scale than local area networks. A wide area network is generally employed whenever information in electronic form on cables leaves a site, even for short distances. Wide area networks are generally carried over public telecommunications networks.
Because conventional telecoms systems have developed in parallel with conventional datacoms systems, there is a significant mis-match in data rates between conventional datacoms protocols as used in LANs and WANs, and conventional telecoms protocols. In general, telecoms operators provide equipment having standard telecoms interfaces, for example E1, T1, E3, T3, STM-1, which are used by the datacoms industry to provide wide area network point to point links. However, this is inconvenient for datacoms providers since datacoms protocols have developed using a completely different set of interfaces and protocols, for example carrier sense multiple access collision detection CSMA/(CD systems, subject of IEEE standard 802.3, and Ethernet which is available in 10 MBits/s, 100 MBits/s and 1 GigaBits/s versions. Conventional datacoms protocols do not match up very well to conventional telecoms interfaces, for example E1, E3, T1, STM-1 data rates, because of a mis-match in data rates and technologies between conventional datacoms and conventional telecoms.
In order to provide transport of OSI layer 2 datacoms traffic cover a wide area in an efficient manner, the inventors have previously disclosed transport of OSI layer 2 data frames over synchronous digital hierarchy networks (including SONET).
In the applicant's co-pending US patent application entitled “Frame Based Data Transmission over Synchronous Digital Hierarchy Network”, a copy of which is filed herewith, there is disclosed a method of carrying OSI layer 2 frame based data, for example IEEE standard 802.3 carrier sense multiple access/collision detection (CSMA/CD) local area network packets, Ethernet packets, conventional token ring packets, conventional token bus packets, and fiber distributed data interface (FDDI) packets directly over a synchronous digital network. Such disclosed system may provide OSI layer 2 switching functionality such as was previously available in prior art local area networks, but extended over a wider geographical coverage area which has been historically considered to have been provided only by prior art wide area networks.
In the applicant's co-pending US patent application entitled “payload Mapping in Synchronous Networks”, a copy of which is filed herewith, there is disclosed a method and apparatus for containment of OSI layer 2 frame based data into a set of synchronous digital hierarchy (SDH) virtual containers, by rate adapting a plurality of OSI layer 2 data frames by invoking buffering and flow control in a rate adaption means, and mapping the rate adapted OSI 2 data frames directly into a plurality of SDH virtual containers. This process enables a virtual OSI 2 local area network to be constructed across a wide area network supported by a synchronous digital transport layer.
Since data rates used by conventional OSI layer 2 datacoms systems are either higher than data rates of individual virtual containers in SDH systems or fit inefficiently into available faster virtual containers, there is the problem of how to carry higher bit rate OSI layer 2 datacoms traffic in SDH virtual containers, to achieve the result of an OSI layer 2 channel carried over an SDH network.